Click on the email Icon
Along the line of the email address you wish to change click on the change quota link and you can change this up to the limit of your package quota.
If you already are at the limit of your package and your box is full you may need to delete old emails or upgrade your hosting package.
Related knowledge base items.
https://www.astutium.com/knowledgebase/392/How-can-i-upgrade-or-downgrade-my-account.html
https://www.astutium.com/knowledgebase/250/How-do-I-automatically-delete-old-emails-on-CPanel-.html
https://www.astutium.com/knowledgebase/781/Email-taking-up-my-disk-space.html
https://www.astutium.com/knowledgebase/349/How-to-make-Outlook-auto-remove-mail-from-the-server.html
